Electronic generator



.Fume 25, M40. D. J. FEWINGS ELECTRONIC GENERATOR Filed July 16, 1937 PA /P l km 25 Our/ w" Joy/20.5 0F Ode/41. A 7/0 /v INVENTOR DA V/D JOHN FEW/N65 BY g W ATTORNEY Patented June 25, 1940 PATENT OFFICE ELECTRONIC GENERATOR David John Fewings, Chelmsford, England, assignor to Radio Corporation of America, a corporation of Delaware Application July 16, 1937, Serial No. 153

In Great Britain July 21, 1936 5 Claims.

This invention relates to electrical oscillation generator arrangements and more particularly to electrical oscillation generator arrangements'for producing saw-tooth or substantially saw-tooth 5 waves and suitable for use as time bases for cathode ray tube oscillograph, cathode ray television, and like purposes.

Numerous proposals have been made in respect of saw-tooth wave oscillation generators for television and like purposes but great practical difficulties have been experienced with known saw-tooth wave generators as regards the obtaining of rectilinearity, amplitude of sawtooth wave, and short time for fly. back where high frequencies e. g. frequencies of the order of 200 kilo-cycles or more, are in question.

An important object of this invention is to provide saw-tooth Wave generator arrangements capable of supplying substantially rectilinear saw-tooth wave oscillations of suficient amplitude to swing the beam of a high vacuum cathode ray tube over a relatively wide angle with a fly back time never greater than about t; of the sweep time and capable moreover of operating over a wide frequency range. 7

According to this invention an oscillation generator arrangement for producing saw-tooth waves and suitable for use as a time base comprises a soLu-ce of oscillations; a cathode ray tube or electron beam valve having two differently positioned collector electrodes; deflecting means for deflecting the electron beam across said collector electrodes said collector electrodes being so arranged that during each deflection or sweep of the beam it impinges on one of the collector electrodes for only a relatively small fraction of the deflection period; means for applying oscillations from said source to said deflecting means to deflect the said beam; a time base circuit; and means for utilizing short sharp voltage pulses generated by reason of the incidence of said beam upon said one collector elec' trode to control said time base circuit. Preferably said one collector electrode is behind the other collector electrode and said other electrode has a narrow slot which is traversed by the beam during each deflection and through which the beam must pass to reach said one electrode. Preferably also the whole arrangement is such 50 that the beam impinges upon said one electrode during and near those instants of time when the oscillatory wave from the source is passing through zero amplitude. The oscillations from the source may be sinusoidal or approximately sinusoidal but especiallyif the last mentioned ar-.

rangement is adopted the said oscillations may departvery considerably from the true sinusoidal wave shape without introducing deleterious effects.

The invention is illustrated in and further explained in connection with the accompanying drawing, in which Fig. 1 shows diagrammatically one embodiment of my invention using an electron beam tube;

Fig. 2 shows a plan View of one of the electrodes of the electron beam tub-e;

Figs. 3a, 3b and 30 show graphically electrical wave forms for explaining my invention; and

Fig. 4 shows schematically the electrode arrangement of an electron beam tube.

Referring to Figure 1 which shows diagrammatically one way of carrying out the invention, the original source of oscillations is a thermionic Valve or dynatron oscillator represented simply by a rectangle l and adapted to produce an approximately sinusoidal voltage wave, though the said wave may, in the embodiment now being described, depart quite considerably from the sinusoidal, the harmonic content being relatively unimportant. Such oscillators may easily be made in accordance with known principles to cover a frequency range. up to many megacycles. The output from the oscillator is fed, for example, by coupling condensers 2, 3 to the plates 3,

5 of a pair of electrostatic deflector plates provided in a miniature cathode ray tube orelectron beam valve 8. This tube or valve which is purely diagrammatically represented (for example the envelope is shown as rectangular though, in practice, it would not, of course, be of this shape) has a rectilinear cathode 7 immediately behind a slit like gap to in a control electrode 3 of disc form, the slit 8a in the control electrode 8 corresponding approximately in length and width to the length and diameter of the emissive portion of the cathode l. Spaced from and parallelled to the control electrode 53 is a first collector electrode 8 which may, for example, be av disc having an elongated diametrical narrow slit 9a of somewhat less length than the diameter of the disc. This collector electrode is shown in face view in Figure 2. The. slit 9a is parallel to the slit 8a and also parallel to the axis of the cathode 7. On the side of the electrode 9 remote from the cathode l is a further collector electrode Ill which may be in the form of a smaller disc parallel to the electrode 9 and a short distance behind it. Between the electrodes 8 and 9 are the electrostatic deflector plates i, 5

already referred to, these plates being adapted to cause the electron beam which emerges through the slit 8a in the control electrode 8 to sweep across the first collector electrode 9 in a direction at right angles to the length of the slit 9a therein. Suitable operating d-c potentials are applied to the various electrodes of the electron beam valve or cathode ray tube 6 from a source ii the potential supply lead to the first collector electrode 9 including a. resistance l2. The electrode 9 is capacity coupled through a condenser it to the input lead it of any suitable known time. base circuit shown within the broken line rectangle 35. In the actual arrangement of Figure 1 the electrode Q is capacity coupled through condenser it to the control grid I6 of a tricde ll, said grid it being connected to earth through a grid leak 88, the cathode it of the tricde ll being connected to earth through the usual capacity shunted resistance combination 2i) and the anode 2! of the triode being connected to a source (not shown) of anode potential through a resistance 22 and being also connected to earth through a pair of preferably adjustable condensers 26% in series.

In the arrangement of Figure 1 the oscillations from the source i applied to the deflector plates l, 5 will cause the electron beam to sweep across the first collector electrode 9 and during each sweep to pass for a short period of time through the gap 9a in said electrode on to the second collector electrode iii. Each time the electron beam impinges upon the second collector electrode in (that is to say twice per cycle of the oscillations from the source 1) there will be a sharp decrease. in current through the resistance E2 in the lead to the first collector electrode 9 and consequently a sharp rise in the voltage of said electrode. To take a normal case, where the second collector electrode Ill is about 50 volts positive with respect to the first collector electrode i! which is in turn about 500 volts positive with respect to the cathode l, and assuming an electron beam current of half a milliampere a sharp rise of at least 2G volts can reasonably be expected at the first collector electrode 9 each time the beam passes through to the second collector electrode Hi. If, therefore, the voltage wave from the source l is, as shown in Figure 3 at (a), sinusoidal the wave form applied to the control grid iii of thetime base valve ll will be (as shown at (b) in Figure 3) a series of narrow substantially square topped positive voltage impulses and if the electron beam valve or cathode ray tube is symmetrically arranged these impulses may be caused to occur each time the voltage wave from the source through zero. The duration of each positive impulse will depend upon the width of the slot 9a in the first collector electrode 9 and the amplitude ofthe oscillations from the source I since the latter controls the speed of passage of the electron beams across the slot 9a. These impulses applied to the time base circuit cause the latter to produce saw-tooth oscillations (as shown at (c) in Figure 3) of substantially rectilinear form and reasonably good amplitude the fly back periods in this saw tooth wave oscillation corresponding to the positive impulses and the sweep periods being provided by the time base circuit itself. The saw-tooth waves generated may be taken from across one of the condensers 211, it (as shown condenser 2 1) in the anode circuit of the time base circuit valve l1 and may be amplified in any convenient way,

the invention.

preferably by a high fidelity, phase, amplitude and distortion-free or so-called paraphase amplifier represented by the rectangle 25.

If desired, instead of inserting a resistance I2 in the feed lead to the first collector electrode 9 and coupling this electrode to the time base circuit iii a resistance may be inserted in the feed lead to the second collector electrode. With this modified arrangement there will be occasioned at the second collector electrode a series of substantially square topped narrow negative voltage pulses. These may be inverted as to phase by a suitable phase reversing valve and then applied to the input terminals of the time base circuit valve.

The precise collector electrode arrangement above described is not a necessary feature of For example in place of using a small second collector electrode Hl behind a slotted first collector electrode 9 the second collcc'tor electrode may be made larger than the first which may be made unslotted so that the second collector electrode receives the beam when the said beam overshoots the first collector electrode. This arrangement is represented in Figure 4 in which 9 represents the first collector electrode and ID the second. Again the arrangement may be made such that the electron beam is incident upon the second collector electrode more than once per deflection, e. g. there might be two slots in the first collector electrode. The arrangement of Figure l is, however, preferred.

Practically, the upper limit as to frequency to which arrangements as above described are subject, is that imposed by the amplifier 25 for the saw-tooth wave oscillations. The saw-teeth will be substantially rectilinear and since the fly-back? duration is determined by the length of time during which the electron beam is incident upon the second collector electrode Iii (or Hi) this can be controlled at will by varying the amplitude of the oscillations from the original source l. The original source of oscillations can be synchronized in any well known method; such synchronization is particularly easily afiected if a dynatron type of oscillator is employed.

Having described my invention, what I'claim l. The method of generating controlled wave energy which comprises the steps of producing sinusoidal oscillations, controlling the deflection of a focused beam of electrons in accordance with the produced sinusoidal oscillations, producing rectangular wave shape energy impulses from the controlled deflected beam of electrons, storing energy substantially linearly with time, and initiating the discharge of the stored energy by said produced rectangular wave shape energy impulses.

2. The method of generating controlled Wave energy which comprises the steps of producing sinusoidal oscillations, deflecting a focused beam of electrons in accordance with the produced sinusoidal oscillations, producing rectangular wave shape energy impulses from the deflected beam of electrons, storing energy substantially linearly with time, and initiatingthe discharge of the stored energy by said produced rectangular wave shape energy impulses.

3. A saw-tooth wave oscillator comprising means for producing sinusoidal oscillations, means for deflecting a focused beam of electrons in accordance with the produced sinusoidal os- (iii cillations, means for producing rectangular wave shape energy impulses from the deflected beam of electrons, means for storing energy substantially linearly with time, and means for initiating the discharge of the stored energy by said produced rectangular Wave shape energy impulses.

4. A saw-tooth Wave oscillator comprising means for producing sinusoidal oscillations, means for deflecting a focused beam of electrons in accordance with the produced sinusoidal oscillations, means for producing rectangular Wave shape energy impulses from the deflected beam of electrons, means for storing energy substantially linearly with time, and means for initiating the discharge of the stored energy by said produced rectangular wave shape energy impulses.

5. An oscillation generator comprising a cathode ray tube having means to produce a beam of electrons, deflecting means for deflecting the produced beam of electrons, a collector electrode, an apertured diaphragm positioned intermediate the collector electrode and the beam producing means, a source of sinusoidal oscillations, connections from said source of oscillations to said deflecting means for deflecting said beam of electrons across the apertured diaphragmv whereby said beam impacts upon said collector electrode for only a relatively small fraction of the time period of the beams deflection to produce rectangular Wave shape energy impulses, means for storing energy substantially linearly with time, and means to initiate the discharge of the stored energy by the produced rectangular Wave shape energy impulses, and a load circuit energized by the discharged stored energy.

DAVID JOHN FEWINGS. 

